50 SUMMARY OF CURRENT RESEARCHES RELATING TO 



gives off a number of branches. Three transverse anastomoses are to 

 be found in the thorax. 



The brain is proportionately large, and nearly fills the head ; seen 

 from above it is bilobed ; and from the lateral lobes there arise the 

 optic nerves. At the hinder end they are connected with a large 

 cellular mass, which lies on the anterior end of the oesophagus, and is 

 the frontal ganglion of the sympathetic nervous system. The median 

 large lobes of the brain are continued backwards into two nerve-cords, 

 which embrace the oesophagus, and unite below to form the sub- 

 oesophageal ganglion. The large compound eyes contain nume- 

 rous crystalline cones, pigmented at definite intervals ; at the 

 hinder margin three cones are separated off, and these, which are 

 stronger but shorter than the others, are each surrounded by a con- 

 tinuous layer, and, with a projecting stalk, form an eye. In the 

 apterous generations of Pemphigus the optic organ is solely represented 

 by these three cones, the compound eye being aborted, in correlation 

 with their mode of life. The number of joints in the antennae have 

 been wrongly used as a means of separating the genera ; the author 

 finds that there are constantly six joints, for in Pemphigus the winged 

 forms have six and not five. The olfactory pits would seem to serve, 

 not so much for findiug the female as for detecting food. 



In Pemphigus bursarius the separate wax-glands are found at equal 

 distances from one another on the back and sides of the animal ; on 

 the prothorax there are four, on the meso- and metathorax and the first 

 six abdominal segments, six, on the seventh there are four, and on the 

 rest none. The glandular tubes, which form a projection into the body- 

 cavity, have each a cylindrical lumen ; the hollow wax-threads of one 

 gland form a bundle ; the development of these organs is found to be 

 correlated with the abortion of the honey-tubes, and the habitation of 

 galls by their possessors. The remarkable and characteristic sugar- 

 tubes are placed on the fifth abdominal segment, and extend laterally to 

 the hinder end of the body ; they vary in form in different genera, and 

 may be well used as a means of distinction. The hypodermis of the 

 body is continued into them, and secretes a cuticle ; the whole tube is 

 traversed by a muscle which takes its origin from the hinder margin 

 of the sternum of the sixth abdominal segment ; by its contraction 

 the tube is directed forwards, and some of the contained sugar-cells 

 expressed. These last are of some size, and contain a finely granu- 

 lated protoplasm, with nucleus and nucleolus ; they secrete spheres, 

 which, at first small, soon form a large, spherical, highly refractive 

 and variously coloured mass. Under the influence of the air the sugar 

 crystallizes into fine needles, which traverse the cell-wall and form 

 a group outside it. 



With regard to the sucking apparatus, the author is of opinion 

 that the rudiments of the mandibles and first pair of maxillae are not 

 lost, but are sunk into the body, where they form the so-called " retort- 

 shaped organs " ; these, when fully developed, have an outer invest- 

 ment of flattened cells, which is continued into the epidermis of the 

 body, and consists of a compact mass of pretty large nucleated cells, 

 which secrete at the periphery a chitinous substance, which hardens 



